1. Field of the Invention
The invention relates to a sustained-release pharmaceutical tablet consisting essentially of encapsulated drug pellets blended and compressed into tablet form with a compressible tableting mixture and a process for preparation thereof.
2. Description of the Prior Art
Barry U.S. Pat. No. 2,996,431 issued Aug. 15, 1961 discloses a friable tablet composed of a large number of small pellets embedded in a matrix or binder. The pellets are provided with a coating of a medicinal agent in turn sealed by a protective or barrier coating whose thickness or character is such that the protective coatings on different groups of pellets are disintegrated in the alimentary tract at successive time intervals to achieve a sustained action. The matrix or binder into which the pellets are embedded is designed to be readily disintegrable on application of thumb pressure with a twisting motion due to the shearing forces transmitted by the pellets.
Peters et al. U.S. Pat. No. 3,492,397 issued Jan. 27, 1970 discloses a method for imparting sustained-release characteristics to drug-coated pellets by coating the pellets with a combination of wax and ethylcellulose.
Fulberth et al. U.S. Pat. No. 3,835,221 issued Sept. 10, 1974 discloses a delayed-action drug dosage form wherein the active substance is applied onto small sugar globules. The drug-coated globules are provided with a release-delaying coating which is suitable as a dialysis membrane and which contains a film former polyvinyl acetate, preferably in admixture with ethylcellulose. The globules coated with active ingredient and dialysis membrane are then made up into capsules.
Estevenel et al. U.S. Pat. No. 3,922,338 issued Nov. 25, 1975 discloses tablets comprising the association of a plurality of superposed layers of which the medial layer contains microcapsules containing an active substance. The exterior layers which comprise microcrystalline cellulose, starch, alginate or polyoxyethylene glycol constitute means of protecting the microcapsules of the medial layer.
Mony et al. U.S. Pat. No. 3,950,508 issued Apr. 13, 1976 discloses the preparation of delayed-action pharmaceutical tablets from admixtures of active ingredient with talc, ethylcellulose, magnesium stearate and optionally polyvinylpyrrolidone. The mixture of ingredients is granulated and compressed into tablets.
Ogawa et al. U.S. Pat. No. 4,261,970 issued Apr. 14, 1981 from application Ser. No. 109,082 filed Jan. 2, 1980 discloses a sustained-release granule comprising theophylline in combination with the metal salt of a high fatty acid and ethylcellulose. The release rate of theophylline is stated to depend upon the ratios of theophylline, the metal salt of a higher fatty acid and ethylcellulose.
Boehringer Ingelheim British Pat. No. 2,025,227 published Jan. 23, 1980 discloses a pharmaceutical preparation in retard form comprising a core containing an active substance together with a carrier or excipient, said core being coated with a semipermeable coating comprising a water-insoluble film former, e.g. ethylcellulose, and a water-soluble polymer, e.g. polyvinylpyrrolidone. The core may be in the form of a tablet which is then spray-coated with the semipermeable coating.